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Specular vs IOR
show user profile  9krausec
So IOR is how either how the light is bent (for non-opaque objects) or at what angle the light bounces off an object (for opaque objects).

Then you have specular which controls how intense your highlights are.

What is the difference between these two in 3D land? Turning up the IOR increases how intense the highlights are and turning up the specular amount seems to do roughly the same thing (I know there is something I'm missing here).

I usually just mess with both until I get what I want, but I'm wondering why things are the way they are?

- Portfolio-

read 959 times
7/29/2014 5:58:02 PM (last edit: 7/29/2014 5:58:02 PM)
show user profile  Nik Clark
Assuming Max materials.
Specular is a fake. It's not real. It's adding phong highlights to surfaces that face lights.

Real highlights are created by reflection, of which IOR plays a part. The highlight size is what we call the glossiness of the material (the tightness of reflection, as it were).

Ignore the above if you are using a material that is using glossiness for specularity, etc.

read 955 times
7/29/2014 6:03:14 PM (last edit: 7/29/2014 6:07:51 PM)
show user profile  Coxy
IOR decides the falloff of the diffusion of light at varying angles (So straight on something might look matte, but at a glancing angle it may look highly reflective). Specular decides the way the highlight appears visually, but not the physical properties behind how it is produced.
read 939 times
7/29/2014 6:48:17 PM (last edit: 7/29/2014 6:48:17 PM)
show user profile  9krausec
Alright, so then when you are creating a material which one do you use and for what purpose?

Like I said, I use both of them until it looks good but there isn't really rhyme or reason behind it..

Thanks guys. ALSO check this out -

A bunch of decent maps on this site I stumbled across. Might be useful.

- Portfolio-

read 936 times
7/29/2014 6:57:16 PM (last edit: 7/29/2014 6:57:16 PM)
show user profile  Nanne
The terminology here can be a bit confusing, depending on what render engine you are using or what materials.

IOR controls the Reflections and Refractions of the material as you mention at the beginning.

Now there are three different "types" of reflections; Diffuse, Glossy and Specular.

Specular or "Mirror" Reflections are "perfect" reflections that you might see in polished metals and mirrors, hence the name "Mirror Reflections".

Glossy Reflections are reflections where the light rays are bouncing of in slightly different directions giving you a more blurred "mirror image" on your object, like you see in plastics materials. The amount of glossiness can vary from just a tiny bit (even very polished materials do in fact have a slight blurriness in reality) to very glossy; like wood or concrete.

Diffuse Reflection is what gives the object it's colour, that is why we set a Diffuse Color for our materials.

In reality every object does in fact act as a mirror, that is to say they reflect lights, but since most objects are not as polished as mirrors, they have Glossy Reflections and do not give you a perfect mirror image of the world around them. This tend to give white "fussy splotches" on objects, called Highlights, or Specular Highlights. This is in fact a blurry mirrored image of a light source in the scene (like a lamp, or the sun). But this kind of rendering--realistic as it may be--requires ray tracing. Back in the old days when ray tracing was to heavy on the CPU they figured out that since most materials have Glossy Reflections any way, we can simply fake this effect by figuring out where the light is in relation to the object and then place a white "splotch" there on the object and blur it out, it works pretty well for like plastics. That is why you have, for the so called "Standard Material" in 3ds Max a value for Specular Level (how intense the splotch should be) and Glossiness (how small/sharp or large/blurred the splotch should be).

So as Nik said; Specular or Specular Highlights are fake. But there is such a thing called Specular Reflection though, that is to say "perfect mirror reflections".

In both the mental ray Arch & Design Material and V-Ray's VRayMtl there are no settings for Specular Levels, it is just Reflectivity and Glossiness. But the effect can be used any way, I think.

VRayMtl have a Higlight Glossiness setting one can unlock to tweak the Specular Highlight.

And in the A&D material there is a setting that turns of the specular highlight if Area Lights are set to Visible to renderer. The reason is that it would be double up if you got BOTH the ray traced reflection of the light source AND the faked Specular Highlight, that would look strange. There is also a special option to just use the Final Gather and (Specular) Highlights too speed up the rendering of that material; but it only works for really blurry materials, such as concrete or rough wood.

Now Light objects do have an option to turn of Specular as well, which is not necessary for A&D materials as I just said, since that shader has that function built in. In Vray though, I have sometimes been able to get rid of very bright pixels, so called "fire flies", in reflections by turning of Affect Specular in the VRayLight, but I'm not sure how VRay works here, how it handles that kind of thing.

So in short; I'm not sure what you are actually talking about here when you say "Specular", since I don't know what renderer or material you are using. But you should probably stay away from the "Standard Material" in Max and use A&D or VRayMtl, depending on your renderer, and for those materials you don't tweak the Specular, you tweak the IOR and Glossiness. Where IOR is the amount of reflection depending on the viewing angle of the object, and Glossiness is the "blurriness" of the reflections.

I hope it makes sense to you, and I hope I haven't "dumbed" it down to much, perhaps you already knew most of that stuff? In that case, sorry for that :)

Kristoffer Helander
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read 915 times
7/30/2014 3:34:49 AM (last edit: 7/30/2014 4:12:21 PM)
show user profile  Mr_Stabby
IOR doesn't really have much to do with reflections in reality (except in some metamaterials) but it can be used to approximate the simple BRDF curve. glossiness + reflection value + brdf value together make one reflection layer where
reflection value determines the overall strength
brdf determines the reflection strength per angle
glossiness determines the surface perfection(in this case, low values blur the reflection)

this model works fairly well for most materials but real life materials don't have one single reflection layer but rather a whole dimension of it, modulating according to some 12 parameters (the complex brdf model) creating real glossiness (not caused by surface imperfections alone) and blah blah.

specularity is an effect that reacts to light often using the same formula as reflection algorightms, except its much cheaper since it doesn't actually probe its surroundings and produces solid or premapped highlights. Same principles apply though spec + gloss + brdf make one specularity layer. Its not either-or, its all of them that you need to use.

as you turn up IOR you'll notice that the reflections don't just uniformly get stronger but the off angle reflections get more intense while the almost head-on reflections stay the same and exactly head on reflections weaken. thats pretty much all there is to it

read 901 times
7/30/2014 10:36:50 AM (last edit: 7/30/2014 10:43:22 AM)
show user profile  9krausec
Thanks guys for the detailed responses.

Super detailed Nanne, all your info was helpful in understanding more in depth the relationship between the two.

Stabs- "as you turn up IOR you'll notice that the reflections don't just uniformly get stronger but the off angle reflections get more intense while the almost head-on reflections stay the same and exactly head on reflections weaken. thats pretty much all there is to it "


Look at MF go! Yay.

- Portfolio-

read 881 times
7/30/2014 1:39:10 PM (last edit: 7/30/2014 1:39:10 PM)
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